The present invention relates to powered injector systems and methods for use thereof in medical injection or fluid delivery procedures and, more particularly, to control of powered injector systems and methods of controlling powered injector systems.
In many medical diagnostic and therapeutic procedures, a physician or other person injects as patient with a fluid. In recent years, a number of injector-actuated syringes and powered injectors for pressurized injection of fluids such as contrast media have been developed for use in procedures such as angiography, computed tomography, ultrasound and NMR/MRI. In general, these powered injectors are designed to deliver a preset amount of contrast media at a preset flow rate.
Angiography is used generally in the detection and treatment of abnormalities or restrictions in blood vessels. In an angiographic procedure, one obtains a radiographic image of vascular structure with the assistance of a radiographic contrast medium (sometimes referred to simply as contrast) injected through a catheter. The vascular structures in fluid connection with the vein or artery in which the contrast is injected are filled with contrast. X-rays passing through the region of interest are absorbed by the contrast, causing a radiographic outline or image of blood vessels containing the contrast. The resulting images can be displayed on, for example, a monitor and recorded.
In a typical angiographic procedure, a physician places a cardiac catheter into a vein or artery. The catheter is connected to either a manual or an automatic contrast injection mechanism. A typical manual contrast injection mechanism includes a syringe and a catheter connection. The operator of such a syringe adjusts the flow rate and volume of injection by altering the force applied to the plunger of the syringe. Manual sources of fluid pressure and flow used in medical applications such as syringes and manifolds thus typically require operator effort that provides feedback of the fluid pressure/flow generated to the operator. The feedback is desirable, but the operator effort often leads to fatigue. Thus, fluid pressure and flow may vary depending on the operator's strength and technique.
Automatic contrast injection mechanisms typically include a syringe connected to a powered injector having, for example, a powered linear actuator. Typically, an operator enters into an electronic control system of the powered injector a fixed volume of contrast material and a fixed rate of injection. In many systems, there is no interactive control between the operator and the powered injector, except to start or stop the injection. A change in flow rate in such systems occurs by stopping the machine and resetting the parameters. Automation of angiographic procedures using powered injectors is discussed, for example, in U.S. Pat. Nos. 5,460,609, 5,573,515 and 5,800,397.
U.S. Pat. No. 5,800,397 discloses an angiographic injector system having both high pressure and low pressure systems. The high pressure system includes a motor-driven injector pump to deliver radiographic contrast material under high pressure to a catheter. The low pressure system includes, among other things, a pressure transducer to measure blood pressure and a pump to deliver a saline solution to the patient as well as to aspirate waste fluid. A manifold is connected to the syringe pump, the low pressure system, and the patient catheter. A flow valve associated with the manifold is normally maintained in a first state connecting the low pressure system to the catheter through the manifold (and disconnecting the high pressure system from the catheter and the low pressure system). When pressure from the syringe pump reaches a predetermined and set level, the valve switches to a second state connecting the high pressure system/syringe pump to the catheter, while disconnecting the low pressure system from the catheter (and from the high pressure system). In this manner, the pressure transducer is protected from high pressures. See Col 3, lines 20–37. However, compliance in the system components (for example, expansion of the syringe, tubing and other components under pressure) using such a manifold system can lead to a less than optimal injection bolus. Moreover, the arrangement of the system components of U.S. Pat. No. 5,800,397 results in relatively large amounts of wasted contrast and/or undesirable injection of an excessive amount of contrast when the low pressure (saline) system is used.
The injector system of U.S. Pat. No. 5,800,397 also includes a handheld remote control connected to a console. The control includes saline push button switches and a flow rate control lever or trigger. By progressive squeezing of the control trigger, the user provides a command signal to the console to provide a continuously variable injection rate corresponding to the degree of depression of the control trigger.
Similarly, U.S. Pat. No. 5,916,165 discloses a handheld pneumatic controller for producing a variable control signal to control a rate of fluid dispersement to the patient in an angiographic system. U.S. Pat. No. 5,515,851 discloses an angiographic system with a finger activated control pad to regulate the injection of fluids.
Unlike manual injection systems, however, there is little if any feedback to the operator of system pressure in the above systems. There are potential advantages to such feedback. In the use of a manual syringe, for example, excessive backpressure on the syringe plunger can provide evidence of occlusion of the fluid path.
U.S. Pat. No. 5,840,026 discloses, among other things, an injection system in which an electronic control system is connected to the contrast delivery system and a tactile feedback control unit. In one embodiment, the tactile feedback control unit includes a disposable syringe that is located within a durable/reusable cradle and is in fluid connection with the fluid being delivered to the patient. The cradle is electrically connected to the electronic control system and is physically connected to a sliding potentiometer that is driven by the plunger of a disposable syringe.
During use of the injection system of U.S. Pat. No. 5,840,026, the doctor holds the cradle and syringe and, as the doctor depresses the sliding potentiometer/syringe piston assembly, the plunger is moved forward, displacing fluid toward the patient and creating a pressure in the syringe. A sliding potentiometer tracks the position of the syringe plunger.
The electronic control system controls the contrast delivery system to inject an amount of fluid into the patient based on the change in position of the plunger. As the fluid is injected, the pressure the doctor feels in his hand is proportional to the actual pressure produced by the contrast delivery system. The force required to move the piston provides the operator with tactile feedback on the pressure in the system. The doctor is able to use this feedback to ensure the safety of the injection procedure.
Unlike the case of a manual injection system, the injection system of U.S. Pat. No. 5,840,026 does not require the doctor to develop the system pressure and flow rate. The doctor develops a smaller, manually applied pressure which corresponds to or is proportional to the system pressure. The required manual power output (that is, pressure×flow rate) is decreased as compared to manual systems, whereas the tactile feedback associated therewith is retained.
Although advances have been made in the area of angiographic injection systems, it remains desirable to develop injectors, injector systems and methods to facilitate such procedures.